Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $60.64   8.724%   $65.9302   $65.93   $65.95   $65.90  
  Purchase #2 $232.80   12.342%   $261.5322   $261.53   $261.55   $261.50  
  Purchase #3 $140.97   13.544%   $160.063   $160.06   $160.05   $160.10  
  Purchase #4 $40.97   8.306%   $44.373   $44.37   $44.35   $44.40  
  Purchase #5 $181.26   13.305%   $205.3766   $205.38   $205.40   $205.40  
  Purchase #6 $228.68   11.553%   $255.0994   $255.10   $255.10   $255.10  
  Purchase #7 $115.50   6.212%   $122.6749   $122.67   $122.65   $122.70  
  7 purchase totals = $1,000.82       $1,115.0493   $1,115.04   $1,115.05   $1,115.10